(316n) Numerical Simulation of the Confined Motion of Drops and Bubbles Using a Hybrid Vof/Level Set Method

The motion and deformation of a viscous drop within a cylindrical tube filled with an immiscible Newtonian fluid is numerically studied using a hybrid VOF/level set method. Both buoyancy and pressure driving forces for drop motion are considered. The steady drop shape and mobility, as well as the extra pressure loss due to the presence of the drop, are determined over a wide range of Reynolds and capillary numbers. Different branches of solution for the steady drop shape are identified, depending on the initial drop shape used in the computations. Increasing the Reynolds or capillary number leads to larger shape deformations and higher migration velocities. For sufficiently large capillary numbers, steady drop shapes with regions of negative curvature at the trailing end are found. As the capillary number is increased beyond a critical value, the re-entrant cavity at the trailing end of the drop evolves into a jet of exterior fluid that eventually penetrates the drop and causes it to break up. The dependence of the critical capillary number for drop breakup on Reynolds number and drop size is examined. Computed values of the critical capillary number for drop breakup are compared to experimentally measured values in the case of pressure-driven motion. Computational results are also presented for the case of power-law fluids.